1. Field of the Invention
This invention relates to urinalysis and methods to make urinalysis more accurate, specifically this invention relates to methods to remove interfering substances from urine.
2. State of the Art
The kidneys remove unwanted substances circulating in the blood producing urine, which is excreted from the body. Consequently, diverse waste substances and other substances unwanted by the body find their way into urine for subsequent removal from the body. Urinalysis is the testing of the composition and amounts of waste substances in urine, and provides a tremendously powerful diagnostic tool for the medical profession. However, some of these unwanted substances can hide existing medical conditions, and some others can masquerade as non-existent medical conditions, undermining the usefulness of urinalysis as a medical diagnostic tool. Some of the unwanted substances that find their way into a urine sample are drugs and drug metabolites, given either as medicaments for conditions such as control of pain or nausea caused by chemotherapy, or voluntarily abused by the urine donor.
Recently, various immunoassays and other kinds of tests have been developed turning urinalysis into a powerful diagnostic tool. For example, quantities of drugs of abuse and other indicia of disease or bodily state can easily be detected by urinalysis. Some pharmaceuticals or other chemicals that might have been ingested disturb the sensitive tests making the actual state of the body difficult or impossible to determine. Among the substances that can be detected in urine, and used to diagnose medical conditions in the patient giving the sample, are insulin levels, para-aminohippuric acid, phenol sulfonphthalein, phosphate, arylsulfatase-A, lysosome, urine amylase, total urine estrogens, specific estrogens, progestins, aldosterone, catecholamines, 5-hydroxyindoleacetic acid, cortisol, homovanillic acid, human chorionic gonadotrophin, creatine, urea, uric acid, bilirubin, hemoglobin, hydroxyproline, melanin, porphorins, total protein, acid mucopolysaccharide, copper, glucose oxidase and urine ketone. Removal of the potential masking components of urine can help make the various immunoassays or assays by other techniques, such as isolation followed by gas or liquid chromatography followed by mass spectrometry, more accurate.
One compound that may be found in urine results from the chemotherapy to relieve the distressing symptoms of cancer chemotherapy or voluntary ingestion from abuse is tetrahydrocannabinol. A method for detecting this compound is described in U.S. Pat. No. 5,036,013, issued to ElSohly et al., where various deuterated cannabinoids are synthesized to help determine the quantitative amount of tetrahydrocannabinol in a urine sample. Various methods are described therein. One method in particular involves spiking a urine sample with deuterated tetrahydrocannabinol and analyzing the resultant sample with gas chromatography/mass spectrum.
Another example of the problems created by interfering chemicals in urine is exemplified by the case of ibuprophan. Ibuprophan is a prostaglandin synthetase inhibitor that may be taken in large doses to relive pain and inflammation characteristic of arthritis. When a patient taking these massive doses is subjected to urinalysis, it may mask other drugs of abuse, or may be mistaken for tetrahydrocannabinol. Such a misidentification of a drug of abuse can have devastating personal consequences for the tested patient. Therefore, removal of the masking compound before the test would improve the reliability of the test, and prevent possible liability to those requesting the test.